The man who stood so frequently within a last, solitary blow of wrecking Khan’s career emerged from this palpitating thriller to say: ‘I was hurting Amir all night. Many other fighters would have taken a knee and quit. But he has a huge heart and he wouldn’t let it go.

‘There were so many times I felt I was one punch away from knocking him out but he plain refused to let me finish him.’

Khan will draw strength from that tribute as he heads for a December world title summit against either the winner of the current mini-tournament to find a unified light-welter champion, or the IBF welterweight belt holder Devon Alexander.

What all the acknowledgements of his heroics cannot do, however, is answer the questions which continue to nag at our former champion’s quest for renewed glory.

No, not the one about his chin.

What the most persistent of his critics seem unable to comprehend is the contradiction between their ridiculing of Khan’s punch resistance and his capacity for withstanding a ferocity of bludgeoning which would render a grizzly bear senseless.

‘I think you all saw that Amir can take a punch,’ said his new trainer, with a hint of irony.

In action: Amir Khan shapes up to punch Julio Diaz on the way to victory

Revival: Diaz knocked Khan down in the fourth round, but the Brit got straight back up to win

What Virgil Hunter found more complicated to explain is why Khan is still taking so many heavy hits that there has to be a limit to how many wars like this he can endure.

There may come a point where he is too brave for his own good.

This is only their second fight together and Hunter is demanding more time with Khan than merely their pre-bout training camps near San Francisco. So the jury is out.

But against Diaz there was little sign as yet of Khan protecting himself any more securely than he did under Freddie Roach.

He did display an occasional, new-found willingness to hold or run to give himself time to recover from disorientating damage but surely it is not merely to improve on such basics that a boxer leaves one world-class trainer for another.

And when the intelligent Diaz spoke of how Khan escaped him he credited the Englishman’s traditional, instinctive willingness to fight back in adversity, saying: ‘Whenever I went for the finish he caught me on the way in with stinging punches of his own. He was at his most dangerous when he was hurt.’

There have to be doubts as to whether it is possible to fundamentally change a boxer more than seven years into a career which has already yielded two world titles Even though Khan is still only 26 time appears to be pressing.

A revenge match against Danny Garcia is high among Khan’s priorities and that possibility came closer as the American who knocked him out three fights ago earned a hard-fought victory over Zab Judah later on Saturday night.

Garcia is now scheduled to meet the winner of next month’s second semi-final of that mini-tournament, Lamont Peterson or Lucas Matthysse, this summer to set up the mid-winter showdown with Khan.

Thereafter, to avoid further corrosive battles of attrition, it might be better for Khan to go straight to a mega-fight with Floyd Mayweather next spring rather than take a warm-up as he ascends to welterweight.

If that is how it pans out, he will be going into the defining moment of his career only three fights into his relationship with Hunter. After the first two he looks only slightly different, not significantly better.

On that basis, they might more wisely devote whatever time they can find together to fine-tuning the natural-born fighting qualities which, for all the risks, make Khan so exciting to watch as well as such good box office here and in America.

And, by the way, still one of the best fighters in the world. As Garcia says: ‘His speed, not only of hand but of foot, is his power and makes him very uncomfortable for anyone to box.’

Strike a pose: Khan and Diaz in action on the way to the Brit's unanimous points victory

None of those who paid for tickets at
Sheffield’s Motorpoint Arena or subscribed to the BoxNation television
channel received anything less than full value for money.

They saw Khan’s trademark speed
dominate the opening rounds until he was put down in the fourth by two
left hooks in quick succession. He recovered to win more rounds with his
rapid-fire combinations and open a cut beside Garcia’s right eye before
being rocked once more in the eighth.

Again he survived and came back to win
the ninth. Again he was staggered in the tenth as Garcia teed up an
11th round onslaught of scary ferocity but without quite securing the
knock-out he needed.

The Mexican was as courteous as he,
too, was courageous, accepting the decision against him without demur
and saying: ‘While Amir was winning rounds I was going for the knock-out
and letting points slip. I thought I could break him down but he too is
a warrior.’

Brave Murray edged out by Martinez

Martin Murray came as agonisingly close to a spectacular upset as Amir Khan to a nasty shock on a stupendous Saturday night’s boxing on both sides of the Atlantic.

The reformed ex-convict from St Helen’s knocked down the great Sergio Martinez in his home city of Buenos Aires on his way to narrow defeat.

What was intended as a show-case homecoming for Argentina’s world middleweight champion in front of 50,000 fans in a football stadium turned into another Battle of the River Plate.

Murray caught Martinez in the eighth, then almost caught him on the scorecards as his strength and determination pushed the 38-year-old superstar to the limit.

The improvement in Murray’s character as well as his boxing showed when was as accepting of marginal defeat as Julio Diaz had been by Khan in Sheffield a few hours earlier.

Like Diaz, Murray agreed that he had been too wasteful in the early rounds and would have come up just short even if a second fall by Martinez in the tenth had been ruled a knock down rather than a slip in the rainy conditions.

Despite painful memories of how he was robbed by Alex Sturm in his previous bid for a world title, Murray gallantly accepted: ‘Sergio beat me fair and square.’

As did America’s formidable world heavyweight prospect Deontay Wilder against Audley Harrison in Sheffield, albeit more spectacularly.

Wilder’s 28th straight knock-out inside four rounds was delivered barely a minute into the first with the huge right hand which finally leaves dear old Audley seriously contemplating the end.

As one GB Olympian considers retiring, another has made an explosive start to his paid career.

London Games bronze medallist Anthony Ogogo looked every strapping inch a professional in the making as he stopped middleweight journeyman Kieron Gray in the second.